Elevator systems include a variety of control devices to maintain control over movement of the elevator car. A motor causes desired movement of the elevator car to carry passengers to their intended destinations. A brake associated with the motor prevents the elevator car from moving when it is stopped at a landing requested by a passenger, for example. The brake associated with the motor is used to limit the movement or speed of the elevator car under most conditions.
It is possible for an elevator car (or counterweight) to move at a speed that is above a desired speed. Elevator systems include auxiliary brakes that are sometimes referred to as safeties for stopping the elevator car if it is moving above the desired speed. Some safeties have a fixed wedge and a moveable wedge that engage opposite sides of a guide rail for stopping the elevator car. Sometimes the forces associated with engaging the guide rail and stopping the elevator car are so large that they exceed the torque of the motor, which makes it difficult to move the car once the safety is engaged. It is desirable to be able to use the motor to cause the elevator car to move upward for releasing the safeties from the guide rails. When the fixed wedge is tightly wedged against the rail under many conditions, the torque of the motor is insufficient to cause such movement of the elevator car. It is then necessary for a mechanic to manually release the safety before the elevator car can be returned to service.